1. Field of the Invention
The field of the invention is laser alignment systems, and more particularly remote indicators for the main receivers of such laser alignment systems.
2. Description of the Prior Art
Laser alignment systems are well known in the industry, primarily for use at construction sites to establish a level plane. Several such systems have been described, for example in U.S. Pat. No. 3,588,249 and co-pending applications Ser. No. 788,800 and Ser. No. 788,764 by the assignee of the present invention. In a typical application, a central transmitter projects laser light in a precise, level, 360.degree. alignment plane established at the transmitter. One or more main receivers are then used through out the construction site to detect the alignment plane of light and indicate whether the receiver is above, below, or on the alignment plane.
These systems are primarily used in heavy construction areas where obstructions such as excavations or uneven terrain sometimes make it necessary for an operator to mount the receiver on a rod or other device in order to reach the alignment plane. When this is done, the operator can no longer see the indicators on the main receiver. Some main receivers are also equipped with an audible indication of alignment, but because of the high noise levels characteristic of the construction environments in which these devices are used, the audible indication cannot always be relied upon. Some systems therefore provide a capability to attach a remote indicator to the main receiver. This remote indicator can then be mounted in view of the operator during leveling operations.
Both the main receiver and remote indicator are usually battery powered for portability. To limit the power drain on the battery, a Liquid Crystal Display (LCD) is the preferred indicating element for both units due to its greatly reduced power requirement when compared to other indicating elements, for example Light Emitting Diode (LED) displays.
While an LCD provides an advantage in power consumption, there are some problems associated with it. An LCD functions by electrically altering the reflective properties of the figures to be indicated. As such, it does not give off any luminance of its own and must be viewed under ambient light to be readable. In some cases, the remote indicator is used under conditions of reduced ambient light, for example down in an excavation, in a partially completed, unlighted building, or at night. Under those conditions, the function of the remote indicator is greatly impaired.